Formulation

In the formulation process, many combinations of buffer conditions and excipients must be tested for stability and propensity for aggregation. Final selection of the most promising conditions for long-term testing does not necessarily require rigorous thermodynamic characterization, but does benefit from an understanding of multiple properties which reflect various facets of stability. High-throughput DLS is the ideal technique for this, as it can address multiple stability-indicating parameters simultaneously testing thousands of conditions per day:

Stability screening

Aggregation state - formation of aggregates, size distribution and rate of formation. This is the basic DLS analysis.

Thermal stability - how temperature induces denaturing and non-native aggregation. Determined through temperature ramps, monitoring changes in molecular size.

Chemical stability - how buffer composition (pH, ionic strength, denaturing solvents such as guanidine) induces denaturing and non-native aggregation. Determined through composition steps, monitoring changes in molecular size.

Colloidal stability - how surface moieties such as charged residues or hydrophobic patches lead to aggregation, unrelated to changes in tertiary structure. Determined through the concentration dependence of translational diffusion, k D or D1.

With the DynaPro Plate Reader, these measurements takes place in situ in standard 96, 384 or 1536 microwell plates, consuming minimal sample quantities. The same samples may be further tested in the same or other plate-based instruments [e.g., to analyze the temperature dependence of colloidal stability (in the DynaPro) or intrinsic fluorescence (in a spectroscopic plate reader)], making the DynaPro Plate Reader an invaluable tool for formulation screening. A software package enables integration of the instrument with robotic sample preparation and plate placement.

Molecular charge

Another helpful light scattering tool for formulation development is Electrophoretic Light Scattering (ELS). The Mobius™ integrates with an autosampler and the Atlas™ for automated measurement of molecular charge, an important parameter for stability. The measurement takes place in native buffers, even under moderate to high salt conditions. Like the DynaPro Plate Reader, the Mobius offers automated measurement of multiple parameters such as thermal and colloidal stability.

Turbidity/opalescence

Opalescence indicates aggregation and particle formation, reversible self-association (RSA), and liquid-liquid phase separation that leads to undesirable product properties. The DynaPro™ NanoStar™ with microliter volumes provides quick turbidity/opalescence measurements of formulations.